Road surface markings are used on paved roadways to provide guidance and information to drivers and pedestrians. Road surface markings can be formed using mechanical or non-mechanical devices. Mechanical road surface markers may be raised or recessed into the road surface, and can be either reflective or non-reflective. Examples of mechanical markers are Botts' dots and rumble strips. Non-mechanical markers may be formed by paint, thermoplastic, preformed polymer tape, epoxy and other methods.
Thermoplastic markers are some of the most common types of road marking based on their balance between cost and performance longevity. Thermoplastic binder systems are generally based on one of three core chemistries: hydrocarbons, rosin esters, and maleic modified rosin esters (MMRE). Thermoplastic coatings are generally homogeneous dry mixes of binder resins, plasticizers, glass beads (or other optics), pigments, and fillers. These types of markers demonstrate increased durability, lasting 3 to 6 years, and retro-reflectivity.
Thermoplastic pavement markings are used in a hot-melt application process for various types of traffic control indicia. They are normally comprised of alkyd or hydrocarbon based resin systems, although hybrid versions of the materials can be formulated to impart favorable properties of each individual system into one combined system. Typically, thermoplastic pavement marking materials are used on roadways in longitudinal lines as edge and center-lines either as a continuous line or a skipped/dashed line. They can also be used for transverse markings such as stop bars, chevrons, traffic taming markings, bike and pedestrian crossings, railroad crossings, or similar markings. Thermoplastic pavement markings are used on public and private highways, public and private properties, airports, and parking lots.
Thermoplastic pavement are non-reactive coatings systems that are 100% solids materials composed of binder, pigment, glass beads, and inert fillers. Each state, and some cities and counties, govern the type and application of thermoplastic application by specifying the chemical composition and final film properties in terms of field performance over the lifecycle of the marking. Although most governmental agencies have their own internal and independent pavement marking specifications, thermoplastic pavement marking specifications are normally based on some variation of AASHTO M-249, which is a federal specification that sets minimum and basic requirements of the materials to be used. The binder is made up of a combination of rosin or petroleum based resins, plasticizing oils, elastomers, and viscosity and flow modifiers. The pigment for white materials is predominately Type II rutile titanium dioxide. The pigment for yellow materials is an organic based yellow pigment which can be a combination of yellow and red or orange pigments designed to withstand high temperatures and provide excellent UV resistance and weatherability. Glass beads are incorporated into the material so that as the material degrades under UV, water, and traffic exposure the glass beads will become exposed and serve as reflective elements for nighttime visibility while under illumination from vehicles' headlamps. An exemplary compositional range for each component is as follows: binder 18-26%, pigment (TiO2 only) 10-12% for white, N/A for yellow, and beads 30-40%.
Conventional thermoplastic mix is supplied in powdered form, which makes it difficult to load into the road marking machine. The technicians have to strictly follow safety regulations and use special equipment when preparing the marking mix. U.S. Pat. No. 5,972,421 discloses a method for producing pelletized pavement marking mixtures in which each pellet is a homogeneous mixture of the desired thermoplastic composition. More recently, co-pending application Ser. No. 14/329,482 filed on Jul. 11, 2014, discloses a system of producing pelletized thermoplastic pavement marking material, which eliminates or significantly minimizes hazards associated with dust produced by powdered mixes. This application is directed to an apparatus and method of producing the thermoplastic pavement marking material in a pelletized form.
Co-pending application Ser. No. 14/339,023, filed on Jul. 23, 2014, discloses a composition suitable for use as a road marking substance. This composition is formed by mixing a binder mixture with a filler mixture, heating the mixed ingredients while mixing into a homogenous molten mixture and then extruding the molten mixture. The extruded material is cooled, cut into individual pellets, coated with an anti-clumping coating and packaged for use in making a road marking substance in situ. The binder can be alkyd-based or hydrocarbon based. The binder includes rosin resins, wax and a plasticizer, and a hydrocarbon resin is added for the hydrocarbon-based binder. The filler contains titanium dioxide, a pigment (if necessary) and ground calcium carbonate. The pellet coating material can be a member selected from a group containing kaolin clay, calcium carbonate, calcined clay, micronized waxes and other anti-clumping materials or a combination of materials.